Momentum Theorem Research Articles

Research on Impact Prediction Model for Corn Ears by Integrating Motion Features Using Machine Learning Algorithms

The mechanical damage of corn kernels during harvest leads to mildew in the kernel storage process, seriously affecting food safety and quality. Impact force is the primary source of mechanical damage in the corn threshing process, and its accurate detection is of great significance for corn threshing with low damage. A method for the impact force detection of corn ears was proposed in this manuscript. The momentum theorem determined the main factors influencing impact force (weight, falling height, and space attitude). Corn ear weight, falling height, and space attitude were used as experimental factors. The bench test was carried out with the impact force of corn ear as the output variable. During the experiment, piezoelectric sensors were used to collect the impact force of corn ears under different motion states. Then, the impact force detection model was constructed using four machine learning algorithms: multiple linear regression, ridge regression, random forest, and support vector regression. The results showed that the RF algorithm was more suitable for constructing the prediction model of average and maximum impact force when corn ears fall, SD, RMSE, and r were, respectively: 0.9526, 1.2685, 0.9855; 3.8389, 3.6071, and 0.8510. Secondly, the weight characteristics had the most significant influence on the impact force detection of the ear. Therefore, this method can be used as an accurate, objective, and efficient online detection method for impact force.

Research on Temperature–Pressure Coupling Model of Gas Storage Well during Injection Production

Periodic changes in wellbore temperature and pressure caused by the cyclic injecting and producing of gas storage wells affect wellbore integrity. To explore the distribution and influencing factors of wellbore temperature and pressure during gas storage well injection-production processes, based on energy conservation, momentum theorem, and the transient heat transfer mechanism of the wellbore, a temperature and pressure coupling model for gas storage injection-production wellbores was established, and a piecewise iterative method was used to solve the model equations. Compared with the field data, the predicted relative errors of the wellhead temperature and pressure were 2.30% and 2.07%, respectively, indicating that the coupling model has a high predictive accuracy. The influences of the injection-production conditions, tubing diameter, and overall heat transfer coefficient on the wellbore temperature and pressure distributions were analyzed through an example. When the gas injection flow rate increased by 1.5 times, the bottomhole temperature decreased by 37%. Doubling the overall heat transfer coefficient resulted in a 10% rise in the bottomhole temperature. An increase of 0.3 times in the gas injection pressure led to a 31% increase in bottomhole pressure. With a 1.5-fold increase in the gas production flow rate, the wellhead temperature rose by 28%, and the wellhead pressure dropped by 20%. The research in this paper can serve as a guide for the optimization design and safe operation of gas storage wells.

More considerations about the symmetry of the stress tensor of fluids.

Regarding a recent dispute about the symmetry of the stress tensor of fluids, more considerations are presented. The usual proofs of this symmetry are reviewed, and contradictions between this symmetry and the mechanism of gas viscosity are analyzed for simple gas flows. It is emphasized that these proofs depend on the theorem of angular momentum that assumes that internal forces between any two fluid particles are always along the line connecting them. Without this assumption, from Newton's laws of motion one can only obtain the theorem of angular momentum with an additional term. It is proved within classical continuum mechanics that this additional term represents the total moment of internal forces, and its volume density is similar to the body couple introduced in generalized continuum mechanics. When discrete structure of matter is considered, this term corresponds to the total moment of the forces exerted on the nuclei by the internal electrons. This moment of internal forces may lead to nonsymmetry of the stress tensor and is, in general, nonzero as long as shear stress exists. A nonsymmetrical stress tensor suggested in the literature is discussed in terms of its effects in eliminating the contradictions and simplifying the Navier-Stokes equation. The derivation of this stress tensor for ideal gases based on the kinetic theory of gas molecules is presented, and its form in a general orthogonal curvilinear coordinate system is given. Finally, a possible experimental verification of this nonsymmetrical stress tensor is discussed.

Effect of grit blasting on fatigue behavior of 2024-T3 aero Al alloy

Aiming at the removal of native oxide film on 2024-T3 Al alloy before plasma electrolytic oxidation, the methods to reduce the fatigue damage caused by grit blasting are explored. Effects of the grit size and pressure on surface roughness, residual compressive stress (RCS), and fatigue life of the Al alloy are studied. Increasing grit size and pressure leads to the increase in the surface roughness and RCS. Based on the theorem of momentum and tool cutting principle, mechanism of the grits on the craters and RCS is revealed. It is found that the angularness of the small-sized grit results in the formation of long scratches. The grit with high kinetic energy induces the large craters and high RCS. The craters are the primary fatigue crack initiation source. Moreover, the craters with long scratch and large height lead to the premature fatigue failure of the grit blasted specimens. However, Fatigue behavior is insignificantly affected by the RCS. The results provide new insights into the fatigue deterioration mechanism and life optimization of the grit blasted samples. Consequently, a parameter optimization scheme for the fatigue life of the grit blasted Al alloy is proposed.

Exploring the mechanisms behind dual-peak formation in energy harvesting efficiency of semi-passive flapping airfoils with varied spring stiffness

Flapping airfoil energy harvesting has emerged as a promising paradigm inspired by birds and marine organisms. In this investigation, a semi-passive flapping airfoil device with a predetermined pitching motion was examined using a transient numerical simulation method employing an overlapping grid technique. The impact of the spring stiffness on the energy harvesting characteristics of the flapping airfoil was analyzed through the implementation of the integral momentum theorem and dynamic mode decomposition. The results demonstrated that the efficiency and power curves of the flapping airfoil exhibited a distinctive bimodal M shape in response to variations of the spring stiffness. The initial peak efficiency point, which corresponded to the system's natural frequency in proximity to the pitching frequency, was found to be heavily influenced by the presence of leading-edge vortexes, thereby influencing lift generation. By utilizing the integral momentum theorem, it was determined that the Lamb vector term, fluid acceleration term, and total pressure term predominantly contributed to the lift generation. The emergence of the second peak efficiency point was primarily linked to torque variations induced by trailing-edge vortexes.

A High-Efficiency Theorical Model of Von Karman–Generalized Wagner Model–Modified Logvinovich Model for Solving Water-Impacting Problem of Wedge

The water-impacting behavior of a wedge is often studied in the slamming phenomenon of ships and aircraft. Many scholars have proposed theoretical models for studying the water-impacting problem of a wedge, but these models still have some shortcomings. This study combines Von Karman’s method, the Generalized Wagner Model (GWM), and Modified Logvinovich Model (MLM) to establish a converged theoretical Von Karman-GWM-MLM (VGM) model. The VGM model utilizes added mass to replace the fluid influence, which is derived from the velocity potential and boundary conditions. Considering the influence of impulse, the velocity is determined by the momentum theorem. Subsequently, the pressure, resultant force, and acceleration of the wedge can be calculated. By comparing with the published test data of other scholars, it is found that the velocity, acceleration, pressure, and force of the wedge obtained by the VGM model reached a consensus with experiments. The validity and accuracy of the VGM model are also verified. The efficiency and accuracy of problem-solving are both balanced when using the VGM model. The establishment of the VGM model is significant for solving water-impacting problems related to wedges.

The impact of local wind and spatial conditions on geometry blade of wind turbine

AbstractThe research addresses the pressing need to understand wind conditions for optimal wind energy utilization, a crucial aspect of achieving global energy sustainability. While previous studies have focused on assessing wind energy potential and terrain roughness, gaps persist in understanding how wind and spatial conditions affect blade geometry. Therefore, this study aims to investigate the impact of local wind conditions on wind turbine blade geometry, integrating nonuniform wind inflow due to wind shear into the theoretical model. Through the paper, it explores blade design for varying inflow conditions and analyses the relationship between terrain type and blade designs. A novel approach to wind turbine blade design, utilizing a theoretical model that combines the local momentum theorem with insights from propeller vortex theory was adopted. Through the analysis, the authors demonstrate that variations in terrain significantly influence blade geometry, underscoring the necessity for tailored turbine designs based on local conditions. The findings reveal discrepancies in blade geometry across different turbine capacities and terrain types, offering novel insights into wind turbine performance optimization. By tailoring blade geometry to specific locations enhances resource utilization, offering insights for energy policymakers. The research provides validated methods for optimizing turbine geometric parameters, opening avenues for increased local investment in wind energy and promoting distributed energy development. Illustrated with wind plants examples, the paper concludes by outlining future research directions in this field.

Theoretical Analysis of Light-Actuated Self-Sliding Mass on a Circular Track Facilitated by a Liquid Crystal Elastomer Fiber.

Self-vibrating systems obtaining energy from their surroundings to sustain motion can offer great potential in micro-robots, biomedicine, radar systems, and amusement equipment owing to their adaptability, efficiency, and sustainability. However, there is a growing need for simpler, faster-responding, and easier-to-control systems. In the study, we theoretically present an advanced light-actuated liquid crystal elastomer (LCE) fiber-mass system which can initiate self-sliding motion along a rigid circular track under constant light exposure. Based on an LCE dynamic model and the theorem of angular momentum, the equations for dynamic control of the system are deduced to investigate the dynamic behavior of self-sliding. Numerical analyses show that the theoretical LCE fiber-mass system operates in two distinct states: a static state and a self-sliding state. The impact of various dimensionless variables on the self-sliding amplitude and frequency is further investigated, specifically considering variables like light intensity, initial tangential velocity, the angle of the non-illuminated zone, and the inherent properties of the LCE material. For every increment of π/180 in the amplitude, the elastic coefficient increases by 0.25% and the angle of the non-illuminated zone by 1.63%, while the light intensity contributes to a 20.88% increase. Our findings reveal that, under constant light exposure, the mass element exhibits a robust self-sliding response, indicating its potential for use in energy harvesting and other applications that require sustained periodic motion. Additionally, this system can be extended to other non-circular curved tracks, highlighting its adaptability and versatility.

Quaternion form of the electromagnetic reciprocity theorem

In this paper, the general forms of quaternion electromagnetic field mutual energy-momentum equations (QEMF-MEME) and quaternion electromagnetic field energy-momentum reciprocal equations (QEMF-EMRE) in frequency domain are derived based on the quaternion-electromagnetic-field equations. It has been discovered that QEMF- EMRE is a reflection of the electromagnetic interaction between lagging and leading waves. The real and imaginary parts of scalar, the real and imaginary parts of vector of QEMF-EMRE correspond to the Feld-Tai reciprocity theorem, Lorentz reciprocity theorem, and the two sets of momentum reciprocity theorems, respectively. While, QEMF-MEME reflects the electromagnetic interaction of two sets of lagging waves, and its real scalar, imaginary scalar, real-vector, and imaginary-vector parts are the Feld-Tai reciprocal energy theorem, the reciprocal energy theorem, the two sets of reciprocal momentum theorem.

Research on vibration characteristics of cone valve based on steady state hydrodynamics

The steady-state fluid dynamic force of the cone valve core reduces the stability of the cone valve, thereby affecting its vibration characteristics. This study first derived the formula for calculating the steady-state fluid dynamic force of the valve core using the momentum theorem. Then, the study used the Computational Fluid Dynamics (CFD) method to explore the variation of steady-state fluid dynamic force with the opening degree of the cone valve and the pressure difference at the inlet and outlet. The study also analyzed the steady-state fluid dynamic force of the improved structure cone valve. Combining the CFD calculation results with the established axial vibration and dynamic models of the valve core spring system, a system dynamics simulation model was developed. Innovatively, the study combined experimental and simulation methods to investigate the vibration characteristics of the cone valve and the impact of steady-state fluid dynamic force on these characteristics. The experimental results aligned well with the simulation results, showing that the influence of steady-state fluid dynamic force on vibration characteristics is similar to that of spring force. At a small opening degree, the compensation structure of steady-state fluid dynamic force can reduce axial vibration amplitude. Increasing the inlet pressure from 2.0 MPa to 2.5 MPa results in a decrease in axial amplitude and an increase in the numerical value of the vibration balance position. Increasing the outlet pressure from 0.5 MPa to 0.9 MPa initially decreases axial amplitude and axial waveform factor, followed by an increase. Increasing the spring preload from 9.4 mm to 13.4 mm leads to a decrease in the numerical value of the balance position, a reduction in amplitude, and a decrease in the waveform factor of the axial vibration of the valve core. The study reveals systematic effects of inlet pressure, outlet pressure, and spring preload on the vibration characteristics of the cone valve. The research results in this paper can provide theoretical support for the structural design of hydraulic valves, reduce the impact of fluid dynamics on vibration, and thereby improve the stability of hydraulic system operation.

Research on performance state evaluation of circuit breaker energy storage spring based on intelligent algorithm

The performance state evaluation method of circuit breaker energy storage spring mainly judges its performance state indirectly by measuring the pre-tightening force or pre-pressure of the spring. However, there may be some errors in this indirect measurement method, which will affect the accuracy of the evaluation results. Therefore, the performance state evaluation based on intelligent algorithm is proposed. Select the evaluation characteristic quantity of performance state, calculate the energy storage spring impulse according to the momentum theorem, and obtain the pressure value of the closing energy storage spring through the pressure sensor as the evaluation quantity reflecting the energy storage spring performance state. The BP neural network is established, and the fireworks algorithm is applied to the BP neural network to optimize the initial weight and threshold, so as to realize the performance state evaluation of energy storage spring based on BP neural network. The experimental results show that the spring energy release speed of the proposed method is in the range of 0 - 1.0m/s, and the estimated spring pressure value is basically consistent with the actual value.

Numerical study on hydraulic characteristics of rotating stepped dropshafts in deep urban tunnels.

As an important component of the deep tunnel drainage system for dealing with urban waterlogging, the rotating stepped dropshaft has been proposed due to its small air entrainment. However, the hydraulic characteristics inside the shaft still need to be fully studied. In this study, the flow patterns, water velocity, and pressure in the rotating stepped dropshaft under different flow rates and geometric parameters were studied using a three-dimensional numerical model. The results show that increasing the central angle of the step and reducing the step height can both reduce the terminal velocity. A theoretical formula for predicting the terminal velocity was established and well validated. The connection between the shaft and the outlet pipe poses a severe threat to the structural safety due to alternating positive and negative pressures. Wall-attached swirling flow generates a circular high-pressure zone at the bottom of the dropshaft and the larger the flow rate, the greater the pressure gradient at the center of the bottom. By using the momentum theorem and considering the impact pressure range of the swirling flow, the shaft bottom pressure can be predicted reasonably well.

Optimised design of downhole turbodrills with bending-torsional tilting blade

Deep dry hot rock mining drilling operations confronts several challenges including the high-temperature conditions in the downhole environment, the unreliable performance of surface drives, and the difficult drillability of geothermal reservoir rocks. As a result, the use of downhole motors in drilling operations becomes an imperative selection. The all-metal turbodrill presently stands as the sole downhole motor capable of effectively drilling in deep wells with temperatures exceeding 180°. Although it can withstand high temperature, the output torque is small. In this study, we focus on the optimised design of the turbodrill blades with the objective of enhancing the output torque, addressing the prevailing issue of limited output torque. First, the structural parameters and parametric design are determined based on turbine blade design theory. Utilizing the quintic polynomial method, a two-dimensional blade profile is generated. Subsequently, an output torque model applicable to unsteady flow conditions is derived using the moment of momentum theorem in its integral form; Utilizing the designed blade profile, the Unigraphics NX (UG) software is used to illustrate the combination of spatial twisting, bending and tilting of the blade for the combination of the modelling method, and a three-dimensional bending-torsional tilting blade was achieved. Subsequently, numerical analysis, employing Computational Fluid Dynamics (CFD) simulation software, was conducted to examine the impact of intricate spatial modelling on the blade's flow field parameters. The optimal parameters for blade spatial modelling were ascertained to be a twist lofting radius of 63 mm, a bending angle of 30°, and an inclination angle of 3°. The blade in the hydraulic efficiency is reduced by only 2.7% of the case, the output torque increased by 18.87%, improving the performance of the turbodrill, so that the turbodrill in the geothermal development drilling has a good application prospect.

Impact Force Algorithm and Parameters of Rolling Stone Impact Pier in Mountain Area

In mountainous bridge engineering, the impact of falling rocks on bridge piers is a critical issue. Although various algorithms have been used to calculate impact forces, there is limited research on the impact force algorithm for rolling stones hitting bridge piers. This study, based on the impulse–momentum theorem and the impact force algorithm proposed by professor Ye Siqiao, derived an impact force algorithm for rolling stones hitting bridge piers at different impact velocities and angles. Additionally, an indoor scaled‐down test was designed to analyze the effects of impact velocity, angle, and position on impact force, and the results were compared with domestic and international algorithms and the calculated values of the formula derived in this paper. The results show that at an impact velocity of 3.45 m/s and an impact angle of 30°, the peak impact force reached 16.37 kN, which is a 22% increase from 12.85 kN at 2.83 m/s and a significant 53.9% increase from 10.56 kN at 2.29 m/s. Furthermore, the impact force decreased by 13.8% and 21.73% as the impact angle increased from 30° to 45° and 60°, respectively. These findings underscore the significant influence of impact velocity and angle on impact force, highlighting the necessity for accurate algorithms in engineering applications. The formula derived in this paper yielded results closest to the peak impact force, with errors between the results under each impact condition and the peak impact force fluctuating within an engineering acceptable range of ~10%, indicating that the formula derived in this paper is more accurate and reasonable for engineering applications.

Determination of dynamic component reactions in support bearings of rotor saws for cutting hot rolled (message 1)

A distinctive feature of rotary saws is the process of cutting the workpiece, which takes a very short time. For example, a workpiece with a diameter of 200 mm is cut in 0.2 seconds, while traditional designs of sliding and pendulum saws perform this operation in 10-20 seconds or more. This effect is achieved due to the high speeds of feeding the disc to the cut, exceeding traditional modes by 20 or more times. However, due to the specific cutting conditions, weak links were identified in these designs that require further improvement. One of the factors that reduces the reliability of the saw is the insufficient durability of the bearings of the high-speed disk shaft, which perceives the cutting force. Until now, the reliability issues of rotary saw structures remained unresolved. One of the factors that reduces the reliability of the saw is the insufficient durability of the bearings of the high-speed disk shaft, which perceives the cutting forces. Practice shows that the applied methods of calculating the strength of support bearings do not allow taking into account all possible factors that affect the reliability of bearings in the cutting process. First of all, as it turned out, during operation, the saw blade has radial runout, possibly due to an error when cutting the teeth of the blade and the eccentric landing of the blade on the seat when replacing it. For modern rolling mill production, the issue of strength and reliability of rotary saw designs, which are intended for cutting rolled metal, is relevant. The purpose of this work is to determine the precise values of the reaction forces of the support bearings of the disc shaft. As you know, during long-term operation of the object, the place for landing the cutting disc on the faceplate wears out, sometimes there is an error in the hole when making a new disc. Therefore, there is an eccentricity of the center of gravity of the disk. The presence of this eccentricity is taken into account in the work when determining the required forces using D'Alembert's principle of conditional balancing of forces. Due to the fact that the process of cutting with a circular saw is very short-term, the cutting force is considered the impact force. The magnitudes of the reaction forces in the bearings are determined during cutting using the impact dynamics theorems: the momentum theorem and the kinetic momentum change theorem. By projecting the vector formulas of the principle and theorems on the coordinate axis, the systems of algebraic equations are obtained, from which the horizontal and vertical components of the reaction forces in the bearings are determined both in idle mode and during cutting. Due to the fact that the vector of the centrifugal Dalembert force of inertia of the disk changes its direction, the formulas of the reaction forces at different positions of the center of gravity of the disk were obtained. According to the results of the planned numerical analysis of the problem, graphs of the dependences of the horizontal and vertical components of the pressure forces on the bearings can be drawn from: the eccentricity value, the vertical and horizontal components of the cutting forces, the angular velocity and the position of the disk

A two-dimensional friction-decoupling method based on numerical integration method and momentum theorem

This article introduces a simplified Two-Dimensional Friction-Coupling Model (TDFC) designed for typical surface-to-surface contact friction systems in engineering structures. With the assumption of a constant friction force magnitude within each calculation time step, the alteration of the friction direction of TDFC within each calculation time step can be visualized as the rotation of a circular radius under horizontal bidirectional dynamic loads. This dynamic force analysis approach is referred to as the “Circular making”. It is noteworthy that the friction direction change in each calculation time step demonstrates unidirectional rotatability. Leveraging this rotatability and assuming uniform rotation, the momentum theorem accurately determines the direction of the plane friction acting on the TDFC model at the end of each calculation time step. This allows for the decoupled calculation of plane friction and precise response calculation of the TDFC model. The study verifies the reliability of theoretical assumptions, such as constant friction force magnitude and uniform rotation, with a time step of 0.01 s. Additionally, by introducing an equivalent spring effect to modify the TDFC model, it is observed that the modified TDFC effectively simulates the behavior of the Friction Pendulum Bearing (FPB) under horizontal bidirectional seismic loads. Compared to the ABAQUS finite element model of FPB, the modified TDFC model provides a more efficient approach for rapidly and accurately calculating the response of various FPB types under horizontal bidirectional seismic loads by adjusting parameter values of the modified TDFC model.

Mode transition mechanisms in semi-passive flapping-wing propulsion or energy extraction

To facilitate the smooth transition of operational modes in self-sustaining micro-thrusters, this study focuses on a device employing semi-passive flapping wings. Transient numerical methods are used to analyze the variation of flap energy acquisition and propulsion characteristics with pitching frequency, and the relationship between the dominant vortex structure and the force characteristics is analyzed by using the integral momentum theorem and the dynamic mode decomposition (DMD) method. The results indicate that, under the investigated operational conditions, with an increase in the pitching frequency, distinct wake evolution characteristics were observed. In the energy harvesting operational regime, the wake patterns manifest as 2P + mS, 2S + mS, and mS types. During the transitional phase from energy harvesting to propulsion, the wake patterns shift from 2S + mS to 2S transitional types, eventually leading to the manifestation of a reverse Karman vortex street (2S RBVK). In the propulsion operational regime, the wake patterns consist of a reverse Karman vortex street and asymmetric reverse Karman vortex street phenomena. Simultaneously, it was observed that the transition of flapping-wing performance from energy harvesting to propulsion conditions delays behind the transformation of vortex street structures. This delay is attributed to the necessity for the flapping-wing device to overcome its own resistance before generating a net effective propulsive force. The contributions of unsteady wake to thrust primarily encompass vortex thrust, thrust due to localized fluid acceleration, induced momentum force, and induced pressure force. As the pitching frequency increases, the influence of wake vortices on propulsion also intensifies. The contribution of wake vortices to flapping-wing propulsion is determined by the spatial distribution of Lamb vectors and localized fluid accelerations. The conclusions drawn from the dynamic modal analysis and reconstructed flow field analysis of wake vortices align with the findings of the investigation of wake vortices based on the integral momentum theorem.

Theoretical study on the pressure expansion mechanism of diffused self-pumping hydrodynamic mechanical seal

The pressure expansion performance is the key and basis for the diffused self-pumping hydrodynamic mechanical seal to achieve its good cooling performance, self-cleaning performance, and sealing performance. Using the moment of momentum theorem and Stodola's formula, the pressurization effect of the spiral groove on the fluid was analyzed, and the energy head equation of the work done by the spiral groove on the fluid is established. According to the principle of conservation of energy, the energy equation and Bernoulli equation of the work done by the spiral groove on the fluid are derived, the mathematical expression of the conversion of fluid kinetic energy into hydrostatic pressure in the diffuser groove was established, the energy change and energy distribution problems of the fluid after the work of the spiral groove are clarified, and the pressure expansion mechanism is revealed. Through numerical simulation, the relationship between the fluid pressure at the sealing interface, the position and size of the high-pressure field, the opening force, and the leakage rate under different rotational speeds and the structural parameters of the diffuser groove were explored. Finally, the pressure expansion performance of the ordinary self-pumping hydrodynamic mechanical seal and diffused self-pumping hydrodynamic mechanical seal is compared. The results show that the diffuser groove can effectively convert part of the fluid kinetic energy into pressure energy, improve the opening force of the sealing interface, and have a good pressurization effect on the sealing end face. With the widening of the diffuser groove, the pressure peak of the sealing interface increases, the high-pressure field area continues to expand and tends to expand toward the outer diameter of the seal ring, and the opening force also increases significantly; increasing the depth of the diffuser groove will cause the pressure peak of the sealing interface to become smaller, and the area of the high-pressure field will also decrease rapidly, which is not conducive to improving the opening force of the sealing end face.

Mechanical model and numerical simulation of oblique penetration of projectile into foamed aluminum laminated target

To accurately predict the trajectory and attitude of the projectile obliquely penetrating the laminated aluminum foam target, the penetration resistance function which conclude normal stress, shear stress and friction is established in this paper. Then, we establish the differential equation of the projectile motion combined with the momentum theorem and the momentum moment theorem. Finally, we use finite element software Ansys/Ls-Dyna to simulate the oblique penetration, and the attitude deflection under different initial velocity or different initial attitude angle is emphatically analyzed. The results show that there is a peak of attitude deflection at the beginning of oblique penetration, and the peak is little correlated with initial velocity, but is positively correlated with initial attitude angle. The projectile will deflect three times during oblique penetration, and the variation is “increase-decrease-increase”. When the projectile finally through the target, the value of attitude deflection is negatively correlated with initial velocity and positively correlated with initial attitude angle.

An Incremental Self-Excitation Method for Effectively Identifying Low-Frequency Frequency Response Function of Milling Robots

Abstract Robotic machining efficiency and accuracy are constrained by milling vibrations and chatter. The dynamic characteristics of robots are highly influenced by their poses. Consequently, it is crucial to obtain the robot’s dynamic characteristics in any given pose to mitigate vibrations and prevent chatter during large-range machining. This paper proposes an incremental self-excitation method for effectively identifying low-frequency frequency response functions (FRF) of milling robots. By attaching a mass block at the robot’s end, a fully knowable and controllable excitation increment can be achieved, overcoming the shortcoming of traditional self-excitation methods in capturing the dynamic compliance magnitude. By employing suitable trajectory programming, this method can be executed automatically in the desired poses without the need for manual operations. First, the impulse (moment) of the incremental self-excitation is modeled based on momentum theorem, and the association model of the pulse response increment with the incremental self-excitation is established. To address the issue of sensitivity to noise in the FRF calculation process, the incremental self-excitation is assumed to be a Gaussian pulse, and its identification method is provided. Subsequently, the dimensionality requirement for identifying the nine-item (direct and cross) FRFs is effectively reduced using the modal directionality of milling robots, and the corresponding FRF calculation method is proposed. The rationality of the simplifications and assumptions employed in this method is validated through experiments and calculations. The experimental results in several robot poses show that the proposed method can effectively identify all the direct and cross FRFs in the low-frequency band.